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mini hybrid win!

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: jackssmirkingrevenge » Thu Sep 09, 2010 4:10 am

inonickname wrote:Maybe it's time for some nichrome jack?


Gave it a go here but to no avail.
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Unread postAuthor: POLAND_SPUD » Thu Sep 09, 2010 7:21 am

I've been thinking of using one of those firestarters for ignition:

http://www.youtube.com/watch?v=2RieW2tSxzQ

Don't ask me how to put that into a cartridge :D
Though it would be cool if do find a way to do that - the cartridge could be ignited by a pin striking its base

I think this could be used for slightly larger hybrids - place it inside the chamebr and and use an air cylinder to strike it
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Unread postAuthor: jackssmirkingrevenge » Thu Sep 09, 2010 7:31 am

POLAND_SPUD wrote:Though it would be cool if do find a way to do that - the cartridge could be ignited by a pin striking its base


To be honest one of the things I like about piezo/electronic ignition for cartridges is that they don't require a force to be applied to the base of the cartridge to fire, unlike say a piston pneumatic cartridge that needs the pilot to be struck. This means that the bolt spring can be made weaker and increases the chances of a blowback action working reliably.

I really want to get back on track with the cartridges, might have time to make a prototype if only I could stop playing with the subject of this thread for a few minutes :roll:

Now that I'm confident I can get ignition up to 10x I will probably go back to a smaller "realistic" size cartridge body, the quest now is for a silicone seal than will hold a projectile to 150 psi or so. The mini flies back with a lot of force, so the potential for blowback is clearly there.
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Unread postAuthor: Lockednloaded » Thu Sep 09, 2010 7:50 am

Here was BTBs effort with percussion cap ignition I don't know if he ever got it to work reliably, but it's definitely an option to consider to make your cartridges more fire arm like
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Unread postAuthor: jackssmirkingrevenge » Thu Sep 09, 2010 8:10 am

As explained above, I prefer piezo ignition as it removes the need for any sort of hammer to strike the cartridge for ignition...
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Unread postAuthor: ilovefire » Thu Sep 09, 2010 8:47 am

im curious to know what your chamber volume is? im still waiting to get some proper shots of but i know i can get it to ignite at 10x
do you think it should be strong enough to take that sort of pressure if it doesn't burst the burst disk?
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Unread postAuthor: Heimo » Thu Sep 09, 2010 9:14 am

jackssmirkingrevenge wrote:Tiny, the electrode is almost touching the schrader - it's less than 0.5mm. Before modification is was around 1mm and would not ignite higher than 6x

thanks for the advice, I went ahead and made a spark plug for the one I am busy with,
the spark gap is 0.26mm exactly is that too small? I can always enlarge it a bit again.
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Unread postAuthor: jackssmirkingrevenge » Thu Sep 09, 2010 9:32 am

That looks about right ;)

im curious to know what your chamber volume is?


Currently 18.25mL

do you think it should be strong enough to take that sort of pressure if it doesn't burst the burst disk?


Mine can certainly hold 6x, never had a disk fail to burst at 10x though but signs are that it should hold - though again, this is just a guestimate as I have no data on how the shock and heat of combustion affects the epoxy plugs over time.

Chrony tests soon, watch this space ;)

edit: only had time for one chrony shot at 10x, 755 fps with a 16 grain pellet... that's just over 20 ft/lbs, impressive but I was expecting a little more, for the same pellets it's comparable to the velocities I was getting with my6mm burst disk pneumatic, which had a longer barrel of slightly larger diameter.

I tried it with a double burst disk, visible flash through the endcap and the chamber body got too hot to touch, but the disks held and amazingly the thing didn't blow apart :)

Still haven't tried an 11x mix, I'll give that a go this afternoon, then get on with making the suppressor.

I think I'll make a longer 6mm barrel for it to for mach purposes, it seems a shame to not go for the sound barrier with airsoft BBs now that I have a working hybrid :)

Here's what the completed project might look like, still not clear on electrode attachment.
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Unread postAuthor: jackssmirkingrevenge » Fri Sep 10, 2010 11:16 am

spurred on by the burst disk failure at 10x that left this thing intact, I went for 12x and HAHAAAA!!! 1487 fps with a 16 grain pellet!

Not 100% sure that's a reliable chrony result, but the loss of hearing seems to confirm it :D Still won't make it through 2 sheets of steel though, but given the deformation of the lead on penetrating the first sheet it's hardly surprising. I tried with a 0.177" BB in a foil sabot at 12x and it punched straight through, you can see the entry hole top left in the first photo, and the exit hole in the second.

Yes, I really should make that suppressor before I go completely deaf :D

Edit: in order to put the chrony result into perspective, I did some test shots against the same targets with the same pellets fired from my fully charged FX Monsoon which was doing 850-900 fps, it only penetrated one sheet and the dent left in the second sheet was considerably smaller than those left by the mini hybrid at 12x, so I have no reason to doubt the result. That's over 75 ft/lbs, oh yes :D

Started on the suppressor, I've lopped off 4 inches from the barrel which will hurt performance but make it more "pistol sized" - let's see how effective I can make it :)
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Unread postAuthor: Fnord » Fri Sep 10, 2010 12:20 pm

I think 1487fps is a correct reading. The math works out to around 12% efficiency which is probably about average for most hybrids with shorter barrels. Doesn't steel wool tend to catch on fire when used in a suppressor btw?

Edit to JSR:

Also you'll want to make the exposed copper on the inside of the suppressor as dull as possible. Shiny copper is an excellent heat reflector, even though it conducts well in direct contact. Why not also use globs of thin copper wire instead of steel wool? That would be an extremely efficient heat sink.
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Unread postAuthor: jackssmirkingrevenge » Fri Sep 10, 2010 12:27 pm

Fnord wrote:I think 1487fps is a correct reading. The math works out to around 12% efficiency which is probably about average for most hybrids with shorter barrels.


See the edit above, looks like it is about right. Original barrel length was 18 inches, not so short in terms of calibre/length ratio.

Doesn't steel wool tend to catch on fire when used in a suppressor btw?


I suppose the finer stuff would, but I was planning on using the thicker stuff, that or chicken wire, depends what a rummage in the garage turns up :roll:

edit:

*rummage*

insect screen it is :D
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Unread postAuthor: JDP12 » Fri Sep 10, 2010 1:30 pm

looking great pumped to see what the final pistol result is like!
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Unread postAuthor: jackssmirkingrevenge » Fri Sep 10, 2010 1:47 pm

Here's what I'm playing with right now, the muzzle end has been ported, you can also see the copper tube that will be the suppressor body and the foam disks that will be used to cast the epoxy baffles.

As you can see I've been quite restrained with the porting, mainly because I don't want to hurt performance too much. The hope is that the relatively large suppressor volume and multi-baffle design, together with the copper tube and mesh packing acting as a heat sink, will be enough for good sound suppression.

Also you'll want to make the exposed copper on the inside of the suppressor as dull as possible. Shiny copper is an excellent heat reflector, even though it conducts well in direct contact.


The pipe was salvaged from some old boiler piping at work, it's duller than the Twilight series :)
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Unread postAuthor: POLAND_SPUD » Fri Sep 10, 2010 5:20 pm

well it seems you are doing quite well... I can't wait to see (hear) the results

we wants updates :D
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Unread postAuthor: MrCrowley » Fri Sep 10, 2010 5:55 pm

Congrats on the chrony readings.
My word, that is a large suppressor.

:)
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